strutils: Defer import of pyparsing

This is a slow import and the single user of it, the 'split_by_commas'
helper, does not appear to have any users outside of python-glareclient
(which is a dead project). We might want to remove the user at some
point, but for now simply defer loading of the library.

Change-Id: I91d0c6eec5333a660f995a9d1436e4b068693900
Signed-off-by: Stephen Finucane <sfinucan@redhat.com>

oslo_utils/strutils.py

@@ -23,8 +23,6 @@ import re
 import unicodedata
 import urllib
 
-import pyparsing as pp
-
 from oslo_utils._i18n import _
 from oslo_utils import encodeutils
 
@@ -577,8 +575,13 @@ def split_by_commas(value):
 
     .. versionadded:: 3.17
     """
-    word = (pp.QuotedString(quoteChar='"', escChar='\\') |
+    # pyparsing is a slow import; defer loading until we need it
-            pp.Word(pp.printables, excludeChars='",'))
+    import pyparsing as pp
+
+    word = (
+        pp.QuotedString(quoteChar='"', escChar='\\') |
+        pp.Word(pp.printables, excludeChars='",')
+    )
     grammar = pp.stringStart + pp.delimitedList(word) + pp.stringEnd
 
     try: